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bio website lightandmatter.com
location Fullerton, California
age
visits member for 2 years, 9 months
seen Mar 30 at 19:12

I teach physics at Fullerton College, a community college in Southern California. I have an undergrad degree in math and physics from Berkeley and a PhD in physics from Yale. Back when I was doing research, my field was experimental low-energy nuclear physics.


Oct
27
comment Does our existence cost us energy?
@rijulgupta: In your example, the electric dipole moment D is zero before the neutron decays, and then after the decay it begins to attain nonzero values. This causes a change in the field, which propagates outward as a wave. This is not a static example, since D is time-varying.
Oct
27
comment Big Bang and Spherical Symmetry
@RavindraHV: I am more interested with the big bang model of the universe ... and that does indeed have a starting point . You have this backwards. Big bang models do not have a center.
Oct
27
comment Variance in speed of light
@JanDvorak: I always thought that parallel transport always by default happens along a geodesic... Not sure what you mean when you say "by default." You can parallel transport a vector along any curve. Geodesics are special because they parallel transport their own tangent vectors.
Oct
27
comment How was Newton's third law discovered?
Huygens demonstrated these experiments in London in 1661, which was when Newton was 19 and just beginning his studies at the university, so it seems likely that they did predate his arriving at the third law, although I don't know if there's any evidence that he knew of them beforehand.
Oct
27
comment Can protons in the nucleus of an atom be aligned by electromagnetic fields?
Refining your question a little bit: (1) Nuclei generally do not have permanent electric dipole moments (but see physics.stackexchange.com/questions/76339/… ). Therefore the field of interest would be a magnetic field. (2) The nuclear magnetic dipole moment is not just due to the protons. It's due to both the protons and the neutrons.
Oct
26
comment Variance in speed of light
You can, for example, make optical observations. But those optical observations do not tell you what is "really" happening "now" at some distant location.
Oct
26
comment Normal force and reaction
And kindly explain what they are... What do you mean by "they?" The WP article appears to have been written by people who are not physicists and who use physics terminology in ways that are customary within their field, but are fundamentally not right, for the reasons I've given above.
Oct
26
comment Variance in speed of light
I am seeing the velocity of something while sitting in mh chair... One of the basic conceptual obstacles you need to get over in relativity is that idea that there is something going on "now," which you can determine by what you "see."
Oct
26
comment Normal force and reaction
@rijulgupta: In your example, if you're imagining the picture as hanging on a nail, then the vertical force that holds the picture up is not a force from the wall, it's a force from the nail. The free-body diagram for the picture would show an upward normal force F1 from the nail on the picture, and a downward gravitational force F2 from the earth on the picture. F1 and F2 are not 3rd-law partners. If you would like more detail on this, please post a separate question and I'll give a more detailed exposition.
Oct
26
comment Normal force and reaction
Why is it called normal "reaction" force ? It isn't, at least not in any competent treatment I've seen. In one of my text book NCERT it says "there are mutual contact forces (for each pair of bodies) satisfying the third law. The component of contact force normal to surfaces in contact is called normal reaction" Books are wrong sometimes. This sounds wrong, although I can't be certain without more context. As the book also mentions tension as a type of force This sounds like an incompetently written book, but I can't tell for sure because I don't have a copy.
Oct
26
comment What is the exact definition of center of gravity?
This doesn't address the case of a nonuniform field, which is the only thing that makes the question nontrivial.
Oct
26
comment Normal force and reaction
What we call the normal reaction force is a common name given to the reaction forcs which arises between a body and the surface it is kept on... No, normal forces are not necessarily caused as "reactions" to other forces in the sense of Newton's third law. Newton's-third-law partners are always of the same type, so a normal force is always a reaction to a normal force. As an example where there is no other force besides a normal force, consider a pool ball hitting another pool ball.
Oct
26
comment Why does a CD work as a diffraction grating even with light from a light bulb?
This doesn't answer the question. The question is why it works with incoherent light.
Oct
26
comment Amateur moon laser ranging
Somewhat related: amateur (ham) radio operators sometimes do "moon bounce." They're using the whole moon as a reflector.
Oct
24
comment Does a black hole have an interior or does the spacetime manifold itself end at the event horizon?
@dcgeorge: You're confused re $m\propto r$. You can clear this up for yourself by looking it up in a reliable source.
Oct
24
comment Why are all basic physical measurements ratios?
But a unitless measurement doesn't have to be a ratio. For example, I can count that I have five apples in a bag.
Oct
23
comment How many worlds does the world split into in the Many Worlds Interpretation?
possible duplicate of Many-worlds: how often is the split how many are the universes? (And how do you model this mathematically.)
Oct
23
comment Intuitive understanding of the entropy equation
I don't think this addresses the question. The question is about why we can't redefine temperature through an arbitrary one-to-one function. Nothing you've said in this answer rules out such a redefinition.
Oct
23
comment Intuitive understanding of the entropy equation
related: physics.stackexchange.com/q/48497
Oct
23
comment Intuitive understanding of the definition of entropy
@Trimok: The dimensionlessness of $S/k$ can't be used to infer the exponent of $T$. If we redefined a bunch of stuff, we might just end up with $k$ having different units.